on a classic shape,the original down has a flange covering waste gate, can any one tell me the difference between open bellmouth,and what advantage or disadvantage over standard down pipe.

 

With open bellmouths, the wastegate gases don't have to turn through two 90deg turns before joining the main exhaust gas stream, so are much less restrictive to getting the exhaust gases out of the system.

Even better is having a bellmouth modified by placing a 2 to 3 foot long 'divider' bewteen the exhaust and wastegate i.e. so there's no immediate restrictive turbulence as the WG stream hits the exhaust stream... That said, regular bellmouths are fine.

 

thanks for reply.